The prior art is replete with descriptions of polyamide resins and methods of their preparation. Polyamide resins derived from polymeric fatty acids are widely used as binder components in printing inks and the like because of their properties including good adhesion and toughness; see for example U.S. Pat. No. 3,037,871. One problem encountered is that the polyamides which have conventionally been used in the printing inks are required to be dissolved with specific alcohols or with a combination of solvents consisting of an alcohol and a hydrocarbon solvent; typically, toluene. The use of mixed solvents is a considerable problem because of the need for recovery of the solvents. Furthermore, as a result of more stringent environmental regulations, the printing industry is desirous of using materials which are soluble in a single solvent. Toluene is one solvent that printers are able to readily recover in the printing process. Co-solvents such as alcohol become, in effect, contaminants; therefore, the printing industry desires to have resins which are solvent soluble in toluene alone. Among the other requirements for the resins is that they also have relatively high softening points so that when the paper is heated to remove the solvent, the polyamide does not become tacky and cause adhesion of overlaying layers of papers.
A key to achieving polyamide resins having a high degree of solubility in toluene is to terminate the resin chains during polymerization with a monoamine of a specific class. Chain-termination of certain polyamides with monoamines as a control of molecular weight has been described in the prior art; see for example the description given in the U.S. Pat. No. 3,420,789.
The polyamide resins of the present invention are soluble in toluene and meet the specifications desired of a resin binder in printing ink compositions, finding a use as such a binder component.